1. Field of the Invention
This invention relates generally to the field of wireless communication; and more particularly, to communication networks and improvements afforded to these networks when beam steering techniques via modal antenna systems are used on both communication nodes and wireless subscribers to increase system capacity and mitigate interference therebetween.
2. Description of the Related Art
In the field of wireless communications, a recent technological advancement includes the advent of multi-mode active antennas, or “modal antennas”. A modal antenna is a single port antenna capable of being actively reconfigured between a plurality of antenna modes, wherein the modal antenna is characterized with a distinct radiation pattern in each of the plurality of antenna modes. By using the modal antenna capable of generating different radiation patterns, it is possible to exploit a priori knowledge of antenna nulls and lobes in the different modes for steering the beam to have nulls in dominant interference directions while keeping gain in desired directions. Examples of structures and implementations of the modal antennas are provided in U.S. Pat. No. 7,911,402, entitled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION,” issued on Mar. 22, 2011; the contents of the which are hereby incorporated by reference and are summarized as follows:
FIG. 1 illustrates an example of a modal antenna 100, which includes an Isolated Magnetic Dipole™ (IMD) element 104 placed on a ground plane 108, a first parasitic element 112 coupled to an first active element 113, and a second parasitic element 116 coupled to a second active element 117. The active elements 113 and 117 may include switches that either electrically connect (short) or disconnect (open) the parasitic elements 112 and 116 to the ground plane 108. This structure allows for two different modes of operation with a common frequency corresponding to a first state where the parasitic elements 112 and 116 are shorted to the ground and a second state where the parasitic elements 112 and 116 are open.
FIG. 2(a) illustrates a radiation pattern 204 associated with the antenna 100 in the first state; and FIG. 2(b) illustrates a radiation pattern 208 in the second state, which shows a ninety-degree shift in direction as compared to the radiation pattern 204. Thus, by controlling the active elements 113 and 117 of the modal antenna 100, the operation of two modes can be obtained at the same frequency. The control scheme can be extended for three or more multi-mode operations by incorporating, for example, tunable elements in the active elements for variable control and additional active elements for matching. Further, while a parasitic element coupled to a switch will exhibit two tuning states as the switch is (i) shorted or (ii) opened, another parasitic element being coupled to a variable control active element, such as a tunable capacitor or similar tunable element, will be capable of three or more discrete tuning states, and the resulting antenna will be capable of tuning across a plurality of corresponding antenna modes. Examples of these active elements include switches, tunable capacitors, tunable phase shifters, diodes, micro-electro-mechanical system (MEMS) switches, MEMS tunable capacitors, and transistors including a metal oxide semiconductor field effect transistor (MOSFET), a metal semiconductor field effect transistor (MESFET), a pseudomorphic high electron mobility transistor (pHEMT), a heterojunction bipolar transistor (HBT) or of other suitable technologies.
Although certain examples are provided above, it shall be recognized that the term “modal antenna” is intended to include any single-port antenna system configured to produce a plurality of distinct radiation patterns with each radiation pattern thereof corresponding to a unique mode of a plurality of possible antenna modes. Note that the modal antenna will be characterized with a first antenna radiation pattern when in the first mode, and will be further characterized with a second and distinct antenna radiation pattern when in the second mode. Also note that the modal antenna will produce only a single mode and corresponding radiation pattern at any given time, but that the modal antenna can vary the antenna mode in time to vary the antenna's radiation pattern.
For purposes herein, the term “antenna radiation pattern” is defined as: the variation of the power radiated by the antenna as a function of the direction away from the antenna.
Now, with the above understanding of the modal antenna, we describe the state of the art of communication networks.
For purposes herein, a “communication network” includes: one or more sub-networks of communication nodes, and wireless communication devices configured to communicate with the communication nodes. A communication system may include a subpopulation of communication nodes and wireless devices within a single room, a building, a city block, or other space.
The term “sub-network” is defined as: a group of interconnected communication nodes and wireless communication devices.
The term “communication node” is defined as a central connecting point through which one or more wireless communication devices communicate to form a network. A communication node may include, for example, a WiFi access point (AP) or cellular base station transceiver (BST), including a miniature cellular base station transceiver (mBST) also referred to as a “small cell site” or “personal base station”.
The term “wireless communication device”, is defined as any device configured to communicate with one or more other devices through a wireless network connection. A wireless communication device may include a “mobile device”, such as, for example, a cell phone, tablet, or lap top computer, which is portable. Another example of wireless communication devices includes a wireless computer tower, which is non-portable or “fixed”. The terms “mobile user device” and “mobile device” are a subset of the group of wireless communication devices including those devices which are mobile or portable.
Cellular networks and wireless local area networks (WLANs) are now prevalent in society and have evolved to a level that moderate to high data rate transmissions along with voice communications are stable and reliable over large regions and throughout urban areas. Mobile user devices have progressed to the point of providing not only voice communications and low data rate text and email service, but also high data rate internet connectivity. Continued adoption of mobile devices, and introduction of new uses of cellular networks, such as machine to machine (M2M) applications, have put a strain on the cellular systems in regard to providing consistent service and improved service in terms of higher data rates and less service interruptions from one year to the next. Similar congestion can be found on WLAN networks were large number of users are putting strain on the systems. Continued improvements are sought after to improve communication system reliability as well as better command and control of communication nodes and the mobile devices utilizing these nodes.